X-ray diffraction study of nanocrystalline tungsten nitride and tungsten to 31 GPa

X-ray diffraction measurement determined that a newly synthesized nanocrystalline tungsten nitride (W2 N) has a substantially larger cell parameter than its bulk material. Yet the lattice of a metal nanocrystalline tungsten (W) remained unchanged. High-pressure diffraction study to 31 GPa resolved a much lower bulk modulus of 240 GPa for nanocrystalline W2 N and a relatively unchanged bulk modulus of 307 GPa for nanocrystalline W compared to its bulk material. We found that the metallic bonding of a metal is not affected by reduction of the grain size. The enlarged cell parameter and the relatively low bulk modulus of W2 N reflect the size effect of nanocrystalline W2 N.